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1. The problem statement, all variables and given/known data

A circular disk of radius R and total charge Q has the charge distributed with surface charge density [tex]\eta[/tex] = cr, where c is a constant. Find an expression for the electric potential at distance z on the axis of the disk. Your expression should include R and Q, but not c.

2. Relevant equations

[tex]\eta[/tex]=cr where c is constant

V=(1/4pi[tex]\epsilon[/tex])(Q/r)

V=[tex]\Sigma[/tex]V_{i}

3. The attempt at a solution

So what I did was to sum all V_{i}and i was able to pull (1/4pi[tex]\epsilon[/tex]) and (1/sqrt(z^2+R^2) out which leaves me with Q left in the sum which I know i need to relate to [tex]\eta[/tex] in some way. The problem I'm having here is that I just don't understand how to work with [tex]\eta[/tex]=cr in such a way as to get rid of the constant c in my answer.

I feel like I'm not grasping this problem as a whole so any help would be wonderful. Thanks!

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# Electric potential at point x on the axis of a ring of charge density eta

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